Description
Operating Systems Laboratory (CS39002)
PintOS (Ben Pfaff et al.) [http://pintos-os.org/SIGCSE2009-Pintos.pdf] is a popular
minimal operating used at many Universities – in India and overseas – to train students
in the internal details of the Unix-like operating systems. PintOS is minimal since many
OS capabilities are missing and you will be asked to implement them by modifying the
codebase.
The primary document that we use in this subject was originally written at the Stanford
University [https://web.stanford.edu/class/cs140/projects/pintos/pintos.pdf]. The
more detailed version of PintOS and the projects used in Stanford is here:
https://web.stanford.edu/class/cs140/projects/pintos/pintos.html (This should suffice
to give you a basic overview of PintOS).
This warming-up assignment has two parts: In the first one we ask you to install pintOS
on a virtual machine with all the dependencies. In the second one we ask you to improve
the thread implementation supported by PintOS.
Part-1: Installation of PintOS (20 marks)
We can install PintOS in many operating systems (like Windows, linux, mac) with
slightly different set-up instructions for each platform. However, to ensure the
uniformity of implementation (as well as not limit our ability to help you) we chose to
use virtual boxes for our PintOS assignments.
For installing virtual box you need two things: (i) an operating system image and (ii) a
software like oracle virtual box which can load the image and create virtual operating
system (technically a Type-2 hypervisor).
• Download Oracle virtual box from here:
https://www.virtualbox.org/wiki/Downloads
• Download the image from here: https://www.osboxes.org/ubuntu/#ubuntu14_04-vbox (We will use the “Ubuntu 14.04.6 Trusty Tahr” version)
Open the image using virtualbox, you will be asked to create a virtual machine, we
suggest to assign it more than 2 GB or memory and more than 4 GB of physical storage.
You need to run PintOS in this virtual machine. Within your virtual machine PintOS will
run in a simulator, we will use QEMU for this purpose. In your virtual box follow the
following steps:
Installing PintOS with QEMU:
1. Install qemu
> sudo apt-get install qemu
2. Add a softlink
> sudo ln -s /usr/bin/qemu-system-x86_64 /usr/bin/qemu
3. Download PintOS
http://www.stanford.edu/class/cs140/projects/pintos/pintos.tar.gz
Extract PintOS to home folder (say $HOME)
4. Setup GDBMACROS
Open the script ‘pintos-gdb’ (in $HOME/pintos/src/utils. Find the
variable GDBMACROS and set it to point to
‘$HOME/pintos/src/misc/gdb-macros’.
5. Compile utilities
> cd $HOME/pintos/src/utils
Edit “Makefile” in the current directory and replace “LDFLAGS = -lm”
with “LDLIBS = -lm”
> make
6. Adjust Make.vars
Open the file “$HOME/pintos/src/threads/Make.vars” and change the
last line to: SIMULATOR = –qemu
7. Compile PintOS Kernel
> cd $HOME/pintos/src/threads/
> make
8. Make these three changes in “$HOME/pintos/src/utils/pintos”
a) Change line no. 103 to “$sim = “qemu” if !defined $sim;” to enforce
QEMU as simulator
b) On line no. 259, replace “kernel.bin” to path pointing to kernel.bin
file at “$HOME/pintos/src/threads/build/kernel.bin”.
c) Comment out all the lines in subroutine SIGVTALRM(lines 927 to
935)
9. Open “$HOME/pintos/src/utils/Pintos.pm” and replace “loader.bin” at line
no. 362 to point to loader.bin located at
“$HOME/pintos/src/threads/build/loader.bin”
10. Update PATH
Add below mentioned line at the end of $HOME/.bashrc file:
export PATH=$HOME/pintos/src/utils:$PATH
Restart the terminal or execute
> source $HOME/.bashrc
11. Finally, it’s time to check if you have done everything ok: Run pintOS
> cd $HOME/pintos/src/utils/
Verify installation of pintos using following command.
> pintos run alarm-multiple
This should create 5 threads and sleep for some predefined times.
Deliverables:
You need to show your assigned TA that you installed pintos correctly
and the “pintos run alarm-multiple” is working as expected.
Part 2: Implement an Alarm clock (80 marks)
Problem description:
By default, PintOS kernel provides busy waiting when a thread needs to block.
You need to change the behavior and block the thread till a fixed amount of
timer ticks pass. You will work primarily in the “threads” directory of the PintOS
distribution.
Before you start coding, go through this link:
https://web.stanford.edu/class/cs140/projects/pintos/pintos_2.html#SEC18 .
it will provide you an understanding of the gist and functionalities of each
relevant file.
Task:
Reimplement timer_sleep(), defined in devices/timer.c. Currently the
implementation “busy waits” that is it spins in a loop checking the current time
and calling thread_yield() until enough time has gone by. Here is the description
of the function.
Function: void timer_sleep (int64_t ticks)
Suspends execution of the calling thread until time has advanced by at least x
timer ticks. Unless the system is otherwise idle, the thread need not wake up
after exactly x ticks. Just put it on the ready queue after they have waited for the
right amount of time.
Reimplement the function to avoid busy waiting.
Submission Guideline:
You need to upload a zip containing the files you changed along with a design
document in Moodle. There should be one submission from each group. Name
your zip file as “Assgn3_.zip”. The zip file should contain:
• The files that you changed.
• A design document. You can find the template for design document here:
https://web.stanford.edu/class/cs140/projects/pintos/threads.tmpl.
Fill it up according to your implementation and include it in your zip file.
Grading scheme for part 2:
The total marks for this part of the assignment (80 marks) is divided as follows.
Demo the implementation to your assigned TAs and show that your
code works as intended
30 marks
During demo you need to demonstrate that you have indeed
implemented the algorithm promised in the design document
50 marks
